1. Field of the Invention
This invention relates to acceleration measurement methods using electrostatic-capacity-type acceleration sensors that detect accelerations based on variations in electrostatic capacity (or capacitance).
2. Description of the Related Art
Conventionally, a typical type of an electrostatic-capacity-type acceleration sensor (as disclosed in Japanese Patent Application Publication No. Hei 7-260510) comprises a capacitance detector having a moving electrode and a fixed electrode, which are arranged opposite to each other such that a separating distance therebetween is varied in response to an input acceleration, wherein a switched-capacitor circuit converts capacitance variation due to displacement of the moving electrode into voltage variation so as to detect and output an acceleration signal, and wherein in order to broaden the detection range, a servo circuit is provided so as to hold the moving electrode at a neutral position by feeding back the acceleration signal.
Another type of the electrostatic-capacity-type acceleration sensor (as disclosed in Japanese Patent Application Publication No. Hei 10-206457) comprises a moving electrode and a fixed electrode, which are arranged on a substrate surface such that a facing area therebetween is varied in response to an input acceleration, wherein based on the capacitance realized by the moving electrode and fixed electrode, the capacitance variation due to the displacement of the moving electrode is detected so as to produce an acceleration signal.
The acceleration sensor having the servo circuit makes it possible to broaden the detection range compared with the acceleration sensor not equipped with the servo circuit because the movement of the moving electrode is limited in response to the output of the servo circuit. However, the range of the acceleration realized by the servo circuit stabilizing the moving electrode is limited by the electrostatic attraction and the weight of the moving electrode; hence, it is not easy to broaden the detection range.
The acceleration sensor in which the facing area between the moving electrode and fixed electrode is varied provides only a single kind of variation characteristic with regard to the facing area responding to the input acceleration; hence, it is not easy to broaden the detection range.